Example:
We have today the 06.11.2015 (11-06-2015) and we have two date values 01.11.2015 and 30.11.2015.
Now I want to know how much time has past in percent since the beginning (01.11.2015):
Result: 17 %SQL Source:

select
date_from,
date_until,
case
when trunc(sysdate) < trunc(date_from) then -- not started
'0 %'
when trunc(sysdate) > trunc(date_until) then -- end reached
'100 %'
else -- percent value
trim(to_char(round(((trunc(sysdate) - trunc(date_from))/(trunc(date_until)- trunc(date_from)))*100,0))) || ' %'
end IN_PERCENT_VALUE,
case
when trunc(sysdate) < trunc(date_from) then
0
when trunc(sysdate) > trunc(date_until) then
100
else
round(((trunc(sysdate) - trunc(date_from))/(trunc(date_until)- trunc(date_from)))*100,0)
end IN_PERCENT
from (
select
to_date('01'||to_char(sysdate,'mm.yyyy'),'dd.mm.yyyy') as date_from,
last_day(trunc(sysdate)) as date_until
from dual
union all
select
to_date('01'||to_char(add_months(sysdate,-1),'mm.yyyy'),'dd.mm.yyyy') as date_from,
last_day(trunc(add_months(sysdate,-1))) as date_until
from dual
union all
select
to_date('01'||to_char(add_months(sysdate,-1),'mm.yyyy'),'dd.mm.yyyy') as date_from,
last_day(trunc(add_months(sysdate,+1))) as date_until
from dual
union all
select
to_date('01'||to_char(add_months(sysdate,+1),'mm.yyyy'),'dd.mm.yyyy') as date_from,
last_day(trunc(add_months(sysdate,+2))) as date_until
from dual
union all
select
to_date('01'||to_char(add_months(sysdate,-1),'mm.yyyy'),'dd.mm.yyyy') as date_from,
trunc(sysdate+2) as date_until
from dual
--union all
)
order by date_from, date_until